Abstract: By studying four typical land use types in the east of Hainan Island, the distribution characteristics of soil organic carbon content and the change of carbon density under different land use patterns were analyzed. In order to provide a scientific basis for reasonably optimizing the land use mode of Hainan Island and promoting the sustainable development of agricultural production. The study took the east of Hainan Island as the research area, selected four typical land use types (paddy field, abandoned land, orchard land and rubber forest land) as the research objects. Through field investigation and sampling and indoor test analysis, the distribution characteristics of soil organic carbon content and density under different land use types were studied. The change of land use types can lead to the change of soil bulk density. The results showed that: the average soil organic carbon content of 0-30 cm under four different land use types in the study area ranged from 3.73 to 14.01 g/kg. The average soil organic carbon content of paddy field was the highest, and that of rubber plantation was the lowest. The average soil organic carbon content from large to small was paddy field > abandoned land >orchard > rubber plantation. The average organic carbon density of 0-30 cm soil ranged from 1.74 to 5.86 kg·m^-2; Under the same land use types, the change of soil organic carbon density in each soil layer was basically the same. The change trend of soil organic carbon density and soil organic carbon content of four different land use types were similar, and they all decreased with the increase of soil depth. The soil organic carbon density of the four land use types in 0-20 cm soil layer accounted for more than 65% of the study section (0-30 cm) (69.21%-72.99%). The change of land use types would lead to the change of soil bulk density .Among the four different land use types in the study area, the content and density of soil organic carbon in paddy field were the highest, and the content and density of rubber forest land were the lowest; There were differences in soil carbon input under different land use types, mainly because land use types could affect the exogenous input of soil carbon pool; Under the same natural conditions, there were significant differences in soil organic carbon content due to different land use types. Therefore, Hainan should strengthen the management of rubber forest land, especially the use of organic fertilizer.

Key words: land use types, soil organic carbon content, soil bulk density, soil organic carbon density, Hainan Island